The present invention relates to an improved thermal insulation system for mobile cryogenic tanks and the method of installing the thermal insulation in particular between a lading container vessel and its associated outer protective jacket.
Presently the insulation that is used in the vacuum space between the vessel and the jacket of a cryogenic tank is a perlite powder. However, there are at least two disadvantages associated with this form of insulation. In the first place, this known insulation has a higher thermal conductivity in the (insulation) pressure range of 5000 microns of mercury to atmospheric pressure than the system of the present invention.
Accordingly, one object of the present invention is to provide a thermal insulation for use in cryogenic vessels such as tank trucks, trailers, and railroad cars having a relatively low thermal conductivity especially over a pressure range of about 5000 microns of mercury to atmospheric pressure. This low thermal conductivity over a pressure range even up to atmospheric pressure is important in reducing the heat transfer from ambient to the lading container in the event a shipping vacuum is lost either due to accident or malfunction. This is especially critical in the transportation of hazardous materials or where increased heat transfer may cause premature and excessive venting of the commodity into the atmosphere.
Another disadvantage associated with the use of powder insulation is that the powder tends to settle thus exposing parts of the top of the tank which are uninsulated. This causes an increase in heat transfer to the commodity within the inner vessel. Also, there is no simple way of detecting the settling of this powder insulation. The only way to remedy the situation regarding the powder insulation is to open the jacket and refill the insulation. However, this is a costly and time consuming further additional procedure.
Accordingly, another object of the present invention is to provide a thermal insulation for a cryogenic tank truck wherein the insulation is non-settling providing uniform insulation about the entire tank.
A further object of the present invention is to provide an improved insulation system for use primarily in insulating cryogenic tank trucks, trailers and railroad cars.
Still another object of the present invention is to provide an improved method of insulating a cryogenic tank container.